Method of making tubular workpieces



March 4, 1941.

S. FINDLATER METHOD OF MAKING TUBULAR WORKFIECES Filed Nov. 17; 1937 Patented Mar. 4, 1941 UNITED srares PATENT orncs azsam CBS m!) OI MAKING WOIKPII stem-m I'indlater, mama, r... aaalgnor to National Tube Company, a corporation of New Jersey 5 plug or high mill and, thenreeling the workpiece. The plugor high-mill consists of a pair of grooved 'r'ools with a' mandrel plug positioned. therebetween' so that thewall thickness ofthe pierced shellis reduced by the compressionuto which thewall issubjected, by the rolls pressing the wall against the mandrel plug. The. workpiece, after being passed through the highmill, isturned '90 degrees on its longitudinal axis and passed again through the high-mill to obtain a reduction around its entire circumference. I

Since it is necessary under practical operating conditions to .provide the grooved rolls of the high-mill with an outwardly flared portion at the edges thereof in order to prevent the formation of a flu or flash (due to the fact that all of the metal displaced will not move longitudinally of the tube) it has heretofore been the conventional practice to provide a flared portion of 30 degrees or more on both edges of the groove. This flared portionhas a customary radius of approximately double that of the arc comprising the balance of the roll groove contour. Thus 60 degrees or more on each side of the tube which passes through the high-mill is not reduced. or is only partially reduced; after itsflrst pass through the high-mill, which necessitates its being turned 90 degrees on its longitudinal axis and passed again through the high-mill to roll the uni-oiled portion. While this procedure has been more or less satisfactory for the production of relatively heavy or thick-walled tubes it has not proven satisfactory for light-walled tubes where the drop in, temperature of the workpieces during the interval of preparation for the second pass is sufflciently great to cause a considerable -variation in the unit strength of the metal at dlflerentpoints around the perimeter of the workpiece. The characteristic shape of the tears which have been observed in the tube walls indicates that the variation in displacement and in peripheral speed around the groove has imposed deflnite and severe stresses in the tube wall during the rolling operation. When-the stresses act on a workpiece which, on account of the above mentioned, temperature conditions, varies in unit strength throughout'the cross-section, the combination is often sufflcient to cause failure with consequent cobbling. The nature of this phenomenon .is evident when it is realized that in the conven-,

vthan the groove diameter.

I Application November 1'1. 1931. Serial No. 115.151

" jrclm wtso-szi tional groove contour approximately 60 degrees on each side of the tube section remains unrolled and partially unrolled, after the tube has been given its first pass. 1

It is ob oils that, in the elongation made in 5 the second pass. thepreviously worked portion of the tube section then lying in the flared area a of the groove obtains the majority of its elongain the grooves used for rolling light-walled tubes is reduced to-the minimum consistent with good operation. it being understood that it the flare is reduced too much a fln will be formed on two so sides of the shell which cannot be removed by the subsequent reeling operation. However. the tendency to form a fln can be overcome while still reducing the flare to a considerable extent by maintaining the workpiece as it is pierced at a diameter not more than inch larger than the groove diameter and, where possible, the shell diameter should be the same or slightly less Thus, a portion of, the reduction and elongation is due to the shell being pulled or expanded over the plug by the rolls, the rolls thereby having the triple function of pulling the shell over the plug, confining the periphery of the shell and'also reducing the wall I of the shell by their regular function as rolls. It is to be noted that the position of the pug relative to the center line of the high-mill rolls should be such that any wall reduction made by the rolls is made on the outside diameter of the shell. In other words, the surface of the plug contacted 40 by the billet in and slightly in advance of the working zone should be cylindrical, or at least not smaller, at the point of initial rolling contact, in order to reduce the friction between the shell and the plug. Furthermore, the friction or "bite" afforded by the roll groove surface should be identical for the two high-mill rolls! To accomplish this the analysis, hardness and structure of the rolls should be identical.

It is accordingly 'among the objects of them) present invention to elongate tubular workpieces in a single pass through-a high-mill.

The foregoing and other objects will be apparent after referring to the drawing inwhich:

Figure 1 is a fragmentary elevation of a pair of as high-mill mils which have been constructed in accordance with the teachings of the'invention.

Figure 2 is a view similarto Figure 1 but disclosing'rclls of smaller size, although shown in larger scale;

Referring more particularly to the the latter A designates a pair oi high-mill rolls W having complementary grooves. In the specific illustrated this radius is 1% that of the radius 7 example shown the grooves B have a diameter of 9 /4 inches but it will be understood that'this diameter will vary in accordance with :the, size of the finished tubular article desired. The edge portions X of the grooves areflared or have anaugmented radius over an arc ranging= from 10 d grees for larg'ersizes of tubularl'workpieces'upf to 20 degrees forthe'smaller diameters; con

ventional high-mill practice this arcjis somewhat} larger, it being customarily about 30 degrees for the diameter shown in Figure 2 and the radius,

thereof'about twice the radius of the groove. 1 have found that the radius of this flared portion can be reduced to about 1% to] 1% oi the radius of the groove 13. In the preferred embodiment of the groove 8, without producing any unde- 'sirabl e iln or cverfill which cannot be removed in the reeler and still produce the desired elongation in one pass of the workpiece therethrough. The extreme edges ofthe grooves B are rounded oi! as shown at Y in the drawing to eliminate rolls A to form a in on'the any tendency for the workpiece. I I A more uniform displacement of the metal in I the wall of the workpiece is secured'around its,

entire circumference and a greater percentage f the entire wall is supported between two con- -single pass through the high-mill permits of n trically opposite v I a reelingzoperatidn'; fining surfaces than was heretofore considered feasible. Additional frictional eflort is imparted 1 f to the workpiece by the high surface speed portion of theroll groove, thus reducing the magnitude of the forces required from within the wall of the workpiece to eiiect elongation in the partially rolled section lying in the flared area of s the groove. Since the-elongation can be made in a single pass lighter-walled-tuhular workpieces can be produced r than gwas heretofore possible and total a io -se he wei eder lav.- orable temperature conditions which do not exist where a time interval elapses between the first and second pass '01- the conventional high-mill 1 reduction Furthermore, the elongating in' a additional temperatureinime workpiece at the freelets, thereby; permitting" more effective removal of surface irregularities.

While I have showrifan'd described several specific embodiments of my invention i t-will be n to ma 1 do not wish, to) actly thereto, since various [modifications maybe made without departing fromgtheiscope :ot the T invention, as defined by the following ai Iclaim: I A method of; tubular workpiecesiwhichfi includes .su 'iporting a tube over-an'interiorlydis-*- posed mandrel,compressing saiditube-at.-dia-*' points over'arcuate areas of f g degrees to thereby cause a degrees to slight'overtlll but no'flri at the portionson the exterior of-the tube not under-compressiomsaid last-named step being conducted withoutf' pro- I during any substantialchange in the outside. d1"- ameter of the tube, and subsequently removing surface irregularities and :said 1 slight io'v'erflllsf by "8 

